Electrostiatic wide-angle deflection



Dec. 31., 1940.

K. SCHLESINGER ELECTROSTATIC WIDE-ANGLE DEFLECTIQN Filed July 25, 1938 3Sheets-Sheet l l I V C m 10 f Fig.1

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Dec. 31,1940. K scHLESlNGER 2,227,036

ELECTROSTATI C WIDE-ANGLE DEFLECTION Filed July 25, 1938 3 Sheets-Sheet2 Jnven for Dec. 31, 1940. K. SCHLESINGER ELECTROSTATIC WIDE-ANGLEDEFLECTION Filed July 23, 1938 3 Sheets-Sheet 3 Patented Dec. 31, 1940PATENT OFFICE ELECTRDSTATIC WIDE-AN DEFLEC'IION Kurt Schlesinger, Berlinmesne assignments, t

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, Germany, assig'nor, by Loewe Radio, Inc., a

corporation of New York Application July 23, 1938, Serial No. 220,878 InGermany October 20,1937

In the application Ser. 'No. 203,487 it is pointed out that the lack ofmarginal sharpness occurring in the electrostatic deflection of bundlesof cathode rays can be reduced by applying positive auxiliarypotentials, which increase rapidly with increasing angle of deflection,between the anode and the centre point of the plate circuit and to thelens of the television tube. The two potentials will be referred to asauxiliary plate and auxiliary lens potentials. More recentinvestigations by the applicant has shown that a really perfectsharpness at the edge whilst maintaining in full the quality of theimage point at the centre is only possible if the two auxiliarypotentials are employed simultaneously. In this way a cathode ray tubeisobtained having oscillatory lens and an electrostatic deflectionsystem. The simultaneous use of two pairs of plates is also possible,but leads to considerable complications in deriving the lens-correctingpotential, which then requires to be controlled in two co-ordinatessimultaneously.

Static measurements of the course of the correcting potential dependenton the extent of movement have shown that both of the correctingauxiliary potentials depend on the square of deflection of the cathoderay beam. Generally speaking the extent of the correcting amplitudesvaries for lens and plates. In thecase of tubes with magnetic electronlenses the potential correction of the plates must in any case beconverted by a tube into a current correction for the lens magnet.

The invention will be better understood with the aid of, and theessential features of the invention will be apparent from the followingmore detailed description and the accompanying drawings of which Fig. 1is a diagram showing potential curves,

Fig. 2 illustrates the connections of a television tube withelectrostatic and Fig. 3 illustrates the connections of a tube withelectromagnetic ray focusing, while Fig. 4 shows in two views a specialconstruction of the electrostatic deflecting means.

In Fig. 1 there is shown the connection between deflection, deflectionpotential and auxiliary potential, as measured f or a representativecathode ray tube and system. The deflection a is the abscissa, e thedeflection potential, an the plate aid, and an the auxiliary lenspotential. I

It has already been set forth on a previous occasion that a parabolicauxiliary potential of this kind can be produced without special tubes11 Claims. (01. 250-271 by a single integration of the sawtoothpotential of the deflection circuit. This integration can be performedby charging condensers, but it can also be obtained by excitingtransformers by way of sufficiently large series resistances with a con-5 stant sawtooth current and loading the sameon the secondary side bycondensers.

In Fig. 2 there is shown a typical connection system, in which use ismade of the invention in the case of combined plate and lens aid. The 10sawtooth potential I excites a screen grid tube 2 (pentode). In theanode circuit'of the pen-tode there is provided in the first place arelaxation transformer 3, which operates the two plates 4, 4 of thetelevision tube in pushpull. In order that the transformer will apply anundistorted sawtooth potential to the plates, there must be provided inparallel primary connection a resistance 5, which has a lower resistancevalue than the primary impedance of 3. Secondary, the secondary windingof the relaxation transformer 3'must have a shorter natural period ofoscillationthan the desired relaxation return. Thirdly',there must beprovided in the connection between the centre of the secondary windingand ground, a resistance 6, the impedar'ice of which is greater thanthat of the dispersion and building-up capacities to earth. Otherwisethe secondary winding may commence to oscillatein natural oscillation.To produce the auxiliary potentials supplied simultaneously to the lens1 and the centre of the plates in accordance with the invention there isprovided a second transformer 8. Actually, in principle, twotransformersli of this kind having independent iron cores must beconnected in series, the one servingvto produce the plate auxiliarypotential and the other the lens. It has been found, however, 'thatit ispossible and even desirable to produce the two auxiliary potentialssimultaneously. by means of the one transformer and two secondarywindings 9 and 9 tightly coupled with the primary winding and with eachother. The operation of the auxiliary potential transformer 8is'fundamentally-dilferent to that of the-relaxation transformer 3.Whereas the relaxation transformer 3 is in parallel with a lowresistanceinput 5, i. e. operates under no-load conditions, the auxiliarypotential transformer 8 is required to operate in short-circuit. Forthis purpose'lthere is provided on the primary side a potentiometerw I0,the total resistance of which is always greater than the impedance "ofthe primary winding.

The theoretical explanation for this condition is as follows:

There is to be produced a curve having the form of kt (parabola) fromone having the form of kt (sawtooth). Obviously, therefore, the desiredcurve is the integral of the sawtooth curve. According to the inventionthere can be employed for this purpose two transformers, which in thefirst place are capacitatively shunted on the secondary side, andsecondly, are excited with constant current on the primary side(shortcircuit condition). The short-circuiting of an inductive secondarycircuit by a condenser, the impedance of which is smaller than theimpedance of the secondary winding, i. e. the series connection ofcondenser and self-induction, results, with respect to the potential atthe condenser, in the integral of the secondary current. The latter,however, is the integral of the secondary transformer potential. Theterminal potential at the loading condenser is accordingly thedoubleintegral of the transformer secondary potential. As well known,however, secondary and primary terminal potentials of a transformerunder noload conditions are proportional to one another (transformationratio). In consequence the potential at the load condensers II and H isthe double-integral of the primary terminal potential. It mustaccordingly be sought to make the primary terminal potential equal tothe differential curve of a sawtooth. This is obviously accomplishedwhen an undistorted sawtooth current is passed through a winding actingas inductance, as in this case there is produced as primary terminalpotential the potential di u and this is obviously the differentialcurve of a sawtooth. The double integration on the secondary side isthen accordingly equivalent to the single integration of a sawtooth i(t), such as present in the anode circuit of the pentode 2 in Fig. 2.Under these conditions there accordingly appears at the secondarycondensers H and H a parabolic auxiliary potential, so long as theprimary circuit is traversed by an undistorted current sawtooth and solong as the resistance of i0 is greater than the resistance of 8 on theprimary side.

Owing to the not infinitely short return period of the relaxationoscillations being finite and not zero, departures occur from thissimple theory. It has found that the phase shift of the peak of theparabola in Fig. 1 made necessary on account of the finite return periodcan best be produced by not making the two circuits 9, 9' exactly equal,such as would appear necessary in itself, but by selecting the loadingcondensers H and H to be different. In themselves two windings tightlycoupled together and with a common primary winding are equivalent to onesingle winding, the loads of the two part-windings being connected inparallel with each other. This, however, applies only when theconditions of operation of the two windings, including also the loads,i. e. the currents therein, have the same form and the same phase. Forexample a winding 9 having 1,800 turns with a condenser ll of 1,000micromicrofarads supplies exactly the same potential as a winding 9having 900 turns with a condenser of 500 micro-microfarads together witha second similar winding 9', II, which then also supplies the samepotential. It is accordingly possible in the first place to connectthese two part-windings in the two part-current circuits of anelectrostatic lens 1 and between the anode l2 and the centre 6 of theplates, and the auxiliary potential amplitude can be brought to theproper value on the primary side with the potentiometer H] by theparticular connection as shown (constant primary impedance) or betterstill on the secondary side by an equal and simultaneous variation ofthe two integration condensers II and ll. There is then obtained aconsiderable improvement in the sharpness of the edge, in whichconnection, by means of a positive auxiliary potential preferablyproduced by the power supply apparatus at the resistance I3, filtered bythe condenser l4, thedirect potential value carried by the anodeparabola-equal to a third of the maximum amplitude of the auxiliarypotentialrequires to be replaced in inversely equivalent fashion.

Owing, however, to the stated influence of the relaxation return time itis necessary in accordance with the invention to adjust a de-tuningbetween the two circuits H and II. It is immaterial whether il or II ismade to be greater. The adjustment of the de-tuning preferably occursduring an image transmission or during a test period supplied withsignals by a synchronised point-impulse generator. It has been found,for example, that a doubling of the condenser H in relation to H bringsabout an optimum of marginal correction (11:1,000 micro-microfarads,11'=500 micro-microfarads). These values are naturally of a relativekind; they depend on the number of lines per frame of the picture and onthe no-load potential of the transformer, i. e. on the extent to whichthe transformer can be choked with respect to potential by the condenseruntil it provides the proper correcting potential. It provides theparabolic form immediately, as stated, when the conductive value of thecondenser with respect to the basic relaxation oscillation is greaterthan the conductive value of its secondary winding.

The effect of the de-tuning of the two circuits, as can be recognizedfrom the double-ray oscillograph, is equivalent to a timed displacementof the initiation phase of the secondary potential, taken in relation tothe initiation of the primary potential or of the synchronisationsignal. This is exactly the requirement resulting from the returneffect.

Naturally the principle of combining oscillatory lens and oscillatoryplate can also be applied to television tubes having magnetic lenses.The correcting circuits are, upon the excitation of the coil lens,different to Fig. 2 for the excitation of the electric field lens. In atube having a magnetic lens, the sawtooth can be applied in undistortedfashion to a correcting tube l5, so long as the impedance of the fieldlens in the anode circuit of this tube is greater than the innerresistance of the correcting tube, as in this connection system thecurrent in the field lens is already the integral of the grid potential.

Fig. 3 shows a cathode ray tube together with an alternative means ofsupplying the correcting potentials. In Fig. 3 the plate current flowingto the tube 2 through the potentiometer I0 sets up a potential which istransferred from the primary winding of the transformer 8 to thesecondary winding 9; the secondary winding is shunted by a condenser ll.Induced voltage, therefore, is supplied in series with the potentialssupplied by the terminals marked plus and connected to the condenser I!and to the electrode :IZ. The ,pushpull deflection is supplied.throughrthe-transformer 8. 'L.The.lens coil .is "I'. Theradaptationtube"l5,vso long as the lenscoil :I'represents avery.largeexternalresistance in respect thereof, can be directly.coupled with the undistorted relaxation potential circuit I. In ,thisconnection the tube 15 should preferably be axtriode. If on the other.hand a pentodeis ,used, aspecial integration requires .to be performedby means of parallel condensers or series-coils, as described intheabove.

The numerical constants of the circuits can quite readily be calculated.by. those skilled in the :art, .bearing in .mind .thenecessarycondition :that the.lens fleldshouldhave a focal distance increasing inquadratic proportion to the deflection to the rightand leftofthe centreof the image, 1. e. ,a decreasing refractive power, and

, thatgat :the sametime' there is. to be imparted to thezplates withincreasing deflection. a similar ,positiveaid. In this.connection it isimmaterial from the point of View of theinvention whether the lens.fleld is produced by a magnet coil or .by an electric fleldlens.

The practical tests of the invention hadshown that ,a plate deflectionmade sharp at the edges .bythe method described can :be combinedwithoutinterference with a magnetic deflection effectively verticalthereto. It is accordingly possible to place .an outer deflecting magnetover a con- ;denserdeflection system corrected in the man- 'nerdescribed, insuch amanner that the mag- .netic .fleld traverses the tubeparallel to and coinciding with the electric field. The vertical"deflection of .the cathode .ray thereby brought :about does notinterfere-.with the deflection qualities .of the electric componentproduced. .Thecombination is particularly useful when the electricsystemassumes the rapid line deflection and'the magnetic. system the slowimage deflection. In this way the advantages of both systemsarecombined,and the disadvantages, which consist in the case of. a rapid magneticdeflection in a considerable consumption of power, are avoided. Afurther advantage resides in the simultaneous deflection of bothco-ordinates at .the same location, and the consequent remarkableshortness of the combined deflecting element :in the direction of theray. It is advisable in this case to produce more particularly thedeflecting .plates from iron. A plate constructed in accordance WithFig. 4 has been found particularly suitable. It consists of two parts4a, 4b riveted .one to the other in insulated fashion, wherein the polestin-4a are connected together and. with the anode and do not producedeflection of the beam. Onthe other hand the, plate portions lb, 417 areconnected with the deflecting potentials. The .two; partsare rivetedtogether in insulated fashion. ,If-they are both produced from iron andif the backs of the parts 4a are in close proximity to the glass Wall ofthe tube, the magnetic .fleld has a lower eflective air-pathexternal tothe ray space, because of the, iron of the plates, and the sensitivityof the magnetic-deflection is three times greater. The sharpness of theedge of the magnetic deflection is also considerably improved in adeflection of this nature, as the density of the field is veryhomogeneous and the air gap is relatively short.

Iclaim:

1. In a television apparatus comprising a cathode-ray tube,containing'means for producing a cathoderay, combined with an electronlens for focusing said cathode ray, at .least one pairof electrostaticdeflecting :plates, .and ascreen, and meansfor suppl ing saiddeflectingplates with symmetrical deflectingvoltages: in combination means forautomatically altering the refractive force of'said electron lens inrhythm with the deflection of said cathode-ray beam,-and means.for-superposing on thevoltages of said deflecting plates a correctingpotential varying in rhythm with the deflection ofsaid cathode ray beam.

2. In a television apparatus comprising a cathode ray tube, containingmeans forproducinga cathode ray, combined with an electrostatic;electron lens for focusing said cathode ray, at least one pair ofelectrostatic deflecting plates, and a screen, and means for supplyingsaid deflecting plates with symmetrical deflecting voltages: incombination means for superposing on the poten- .tial of oneof theelectrodes of said electron lens .a correcting potential varying inrhythm with the deflection of said cathode ray beam, and means forsuperposing on the Voltages of said deflecting plates a correctingpotential varying in rhythm with the deflection of said cathode raybeam.

3. In a television apparatus'comprising a cathode ray tube, containingmeans for producing a cathode ray, combined with an electrostaticelectron lens having a plurality of electrodes for focusing said cathoderay, at least one pair of electrostatic deflecting plates, and a screen,means for supplying the electrodes of said electron lens with constantpotentials, said potentials being so adjusted that said cathode ray beamis sharply focused upon the centre of said screen, and means forsupplying said deflecting plates with symmetrical deflecting voltages ofsawtooth waveform; in combination means for superposing on the constantpotential of one of the electrodes of said electron lens a correctingpotential substantially proportional to the integral of said deflectingvoltages, and means for superposing to thevoltages of said deflectingplates a correcting potential substantially proportional to the integralof said deflecting voltages.

4. In a television apparatus comprising a cathode ray tube, containingmeans for producing a cathode ray, combined with an electromagneticelectron lens for focusing said cathode ray, at least one pair ofelectrostatic deflecting plates, and a screen, and means for supplyingsaid deflecting plates with symmetrical deflecting Voltages: incombination means for superposing on the current through the magnet coilof said electron lens a correcting current varying in rhythm withthedeflection of said cathode ray beam, and means for superposing on thevoltages of said deflecting plates a correcting potential varying inrhythm with the deflection of said cathode ray beam.

5. In a television apparatus comprising a cathode ray tube, containingmeans for producing a cathode ray, combined with an electromagneticelectron lens for focusing said cathode ray, at least one pair ofelectrostatic deflecting plates, and a screen, means for feeding themagnet coil of :said electron lens with a constant current, saidconstant current being so adjusted that said cathode ray beam is sharplyfocused upon the centre of said screen, and means for supplying saiddeflecting plates with symmetrical deflecting voltages of saw-tooth waveform: in combination means for superposing on the constant current ofsaid magnet coil a correcting current substantially proportional to theintegral of said deflecting voltages, and means for superposing on thevoltages of said deflecting plates a'correcting potentialsubstantiallyproportional to the integral of said deflecting voltages.

6. In a television apparatus comprising a cathode ray tube, containingmeans for producing a cathode ray including an anode, combined with anelectron lens for focusing said cathode ray, at least one pair ofelectrostatic deflecting plates, and a screen, and means for supplyingsaid deflecting plates with symmetrical deflecting voltages of saw-toothWave form: in combination means for automatically altering therefractive force of said electron lens in rhythm with the deflecting ofsaid cathode ray beam, and further means for superposing on the voltagesof said deflecting plates a correcting potential varying in rhythm withthe deflection of said cathode ray beam, said further means comprising atransformer, the primary winding of which is connected in parallel witha resistance greater than the impedance of said primary winding and isfed with a current of saw-tooth wave form by a variable tapping of saidresistance, the secondary winding of which is connected in parallel witha condenser and connected between the anode of said tube and the middleof the secondary winding of a relaxation transformer.

7. In a television apparatus comprising a cathode ray tube, containingmeans for producing a cathode lray includinglan anode, combined with anelectrostatic electron lens comprising a plurality of electrodes forfocusing said cathode ray, at least one pair of electrostatic deflectingplates, and a screen, means for supplying-the electrodes of saidelectron lens with constant potentials, said potentials being soadjusted that said cathode ray beam is sharply focused upon thecentre-of said screen, and means for supplying said deflecting plateswith symmetrical deflecting voltages of saw-tooth wave form: incombination means for superposing on the constant potential of one ofthe electrodes of said electron lens a correcting potentialsubstantially proportional to the integral of said deflecting voltages,and means for superposing on the voltages of said deflecting plates acorrecting potential substantially proportional to the integral of saiddeflecting voltages, said means for superposing correcting potentialscomprising a transformer the primary winding of which is connected inparallel with a resistance greater than the impedance of said primarywinding and is fed with a current of saw-tooth wave form by a variabletapping of said resistance, said transformer having two secondarywindings each connected in parallel with a condenser, the one of saidsecondary windings ,being connected between the middle of the secondarywinding of a relaxation transformer and the anode of said tube, theother winding being connected between one of the electrodes of saidelectron lens and a source of constant potential.

8. In a television apparatus comprising a cathode ray tube, containingmeans for producing a cathode ray, combined with an electromagneticelectron lens for focusing said cathode ray, at least one pair ofelectrostatic deflecting plates, and a screen, means for feeding themagnet coil of said electron lens with a constant current, said constantcurrent being so adjusted that said cathode :ray beam is sharply focusedupon the centre of said screen, and means" for supplying said deflectingplates with symmetrical deflecting voltages of saw-tooth wave form: incombination means for superposing .on the constant current of saidmagnet coil a correcting current substantially proportional to theintegral of said deflecting voltages, and means for superposing on thevoltages of said deflecting plates a correcting potential substantiallyproportional to the integral of said deflecting voltages, said means forsuperposing a correcting current comprising a triode, the grid of whichis supplied with relaxation potentials of saw-tooth wave form, saidmagnet coil being connected between the anode of said triode and asource of potential and having an impedance greater than the resistanceof said triode.

9. In a cathode ray tube system, a cathode ray tube comprising anenvelope having within the envelope means for forming a focused beam ofelectrons and beam deflecting electrodes, a source of sawtooth waveenergy, means to produce from said wave energy energy representative ofthe time integral of said energy, a source of substantially constantvoltage for actuating said beam forming means, means to supply saiddeflecting electrodes with sawtooth wave energy and a predeterminedportion of said produced energy, and means to supply said beam formingmeans with said constant voltage and a second predetermined portion ofsaid produced energy.

10. A cathode ray tube system comprising a cathode ray tube having anenvelope wherein is first electrode with a predetermined positivevoltage, means to supply said second electrode with a positive voltagehaving a different value than the predetermined value of said firstnamed voltage to develop an electron beam, a target means upon which thedeveloped beam is adapted to impinge, a pair of deflecting platespositioned intermediate said second electrode and the target, a sourceof sawtooth wave energy, an electron discharge amplifier having an inputcircuit and an output circuit, means to supply sawtooth wave energy fromsaid source to the input circuit of said amplifier, a first and a secondtransformer, each of said transformers having at least one primarywinding and one secondary winding, a connection from the output circuitof said amplifier to the primary windings of said first and secondtransformers, connections from the secondary of said first transformerto said deflecting electrodes, a serially connected condenser andresistance element connected to the midpoint of the secondary of saidfirst transformer and to said first named source of voltage, connectionsfrom the secondary of said second transformer to said condenser, meansto superimpose a voltage proportional to the time integral of thesawtooth wave energy upon said voltage supplied to said first electrode,and magnetic deflecting means for producing deflection of electrons atright angles to deflection of the electrons produced by said deflectingelectrodes.

11. A cathode ray tube system comprising a cathode ray tube having anenvelope wherein is contained a source of electrons, a controlelectrode, an anode positioned in register with said electron source andsaid control electrode, means to supply said anode with a predeterminedpositive voltage to produce an electron beam, a target element toreceive the said beam, a pair of deflecting plates positionedintermediate said anode and target, a magnetic focusing coil positionedintermediate said control electrode and said anode, a source of sawtoothwave energy, an electron discharge amplifier having an input circuit andan output circuit, means to supply sawtooth wave energy from said sourceto the input circuit of said amplifier, a first and a secondtransformer, said transformers each having at least one primary Windingand one secondary winding, a connection from the primary winding of saidfirst and second transformers to the output circuit of said amplifier,connections from the secondary of said first transformer to saiddeflecting electrodes, a serially connected condenser and a resistanceelement connected to the midpoint of the secondary of said firsttransformer and to said first named source of voltage,

connections from the secondary of said second transformer to saidcondenser, means to superimpose a voltage proportional to the timeintegral of the sawtooth wave energy upon said voltage supplied to saidfirst electrode, means to supply energy from said source of sawtoothenergy to a second electron discharge amplifier, means to supply theamplified energy to said magnetic focusing coil, and magnetic deflectingmeans for producing deflection of electrons from the source of electronsat right angles to the deflection of the electrons produced by thedeflecting electrodes.

KURT SCHLESINGER.

